[Leica] Noctilux hood

["Fantoni, Ernesto" <Fantoni@PHIBRED.COM>]

LUGers,

I just bought a used Noctilux. Really an impressive lens:tomorrow I'll
go to shoot some rolls, but I've seen already beautiful pictures taken
with this lens and, looking at the number of recent messages, it's one
of the most loved lenses in the M pipeline.
Mine has the old round hood with "windows", but I have a problem with
it:it's almost impossible to block it on the lens and it slowly slips
toward the aperture ring creating problems when moving the ring. Even if
properly inserted (the white point on the hood inserted on the metal
pins and turned left along its path, then gently pulled out a bit) the
assembly is very loose and unsecured.
Is this a common problem? Or is it my lens?
Any tip for fixing it?

Thanks in advance

Ernesto